Year	Years
1970	4.61
1971	4.7
1972	4.8
1973	4.89
1974	4.99
1975	5.09
1976	5.19
1977	5.29
1978	5.39
1979	5.49
1980	5.59
1981	5.69
1982	5.8
1983	5.9
1984	6.01
1985	6.11
1986	6.22
1987	6.32
1988	6.43
1989	6.54
1990	6.64
1991	6.75
1992	6.86
1993	6.97
1994	7.08
1995	7.19
1996	7.3
1997	7.42
1998	7.53
1999	7.65
2000	7.78
2001	7.9
2002	8.03
2003	8.16
2004	8.29
2005	8.43
2006	8.56
2007	8.7
2008	8.84
2009	8.99
2010	9.13
2011	9.27
2012	9.42
2013	9.57
2014	9.72
2015	9.86